Fluorine gas production method and fluorine gas production device

Abstract

Provided is a fluorine gas manufacturing method that can suppress blockage of piping and valves by mist. Fluorine gas is manufactured by a method that comprises: an electrolysis step in which electrolysis of an electrolyte is performed in the interior of an electrolytic cell; a sound intensity measurement step in which the intensity of sound produced near an anode in the interior of the electrolytic cell is measured; and an air feed step in which a fluid produced in the interior of the electrolytic cell during electrolysis of the electrolyte is fed from the interior of the electrolytic cell to an external section via a channel. In the air feed step, the channel through which the fluid flows is switched in accordance with the intensity of the sound measured in the sound intensity measurement step. If the intensity of the sound measured in the sound intensity measurement step is at or below a reference value set in advance, the fluid is fed into a first channel through which the fluid is fed from the interior of the electrolytic cell to a first external section, and if the intensity of the sound is above the reference value set in advance, the fluid is fed into a second channel through which the fluid is fed from the interior of the electrolytic cell to a second external section. The reference value set in advance is in the range 10–60 dB.

Description

[Technical field]

[0001] The present invention relates to a method for producing fluorine gas and an apparatus for producing fluorine gas. [Background technology]

[0002] Fluorine gas can be synthesized (electrolytic synthesis) by electrolyzing an electrolyte containing hydrogen fluoride and a metal fluoride. The electrolysis of the electrolyte generates mist (e.g., electrolyte mist) along with fluorine gas, so the mist is carried along with the fluorine gas sent out from the electrolytic cell. The mist carried along with the fluorine gas turns into powder and may clog the pipes and valves used to send the fluorine gas. This may force the operation of producing fluorine gas to be interrupted or stopped, which has been an obstacle to continuous operation in the production of fluorine gas by electrolysis. In order to prevent the mist from clogging pipes and valves, Patent Document 1 discloses a technique for heating the fluorine gas carrying the mist or the pipe through which the gas passes to a temperature equal to or higher than the melting point of the electrolyte. Patent Document 2 discloses a gas generator having a gas diffusion section, which is a space for roughly collecting the mist, and a filler containing section for containing a filler for absorbing the mist. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 5584904 [Patent Document 2] Japanese Patent Publication No. 5919824 Summary of the Invention [Problem to be solved by the invention]

[0004] However, there has been a demand for technology that can more effectively prevent the clogging of pipes and valves due to mist. An object of the present invention is to provide a fluorine gas production method and a fluorine gas production apparatus that can prevent clogging of pipes and valves due to mist. [Means for solving the problem]

[0005] In order to solve the above problems, one aspect of the present invention is as follows [1] to [5]. [1] A method for producing fluorine gas, comprising electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride to produce fluorine gas, an electrolysis step in which the electrolysis is carried out in an electrolytic cell; a sound intensity measuring step of measuring the intensity of sound generated in the vicinity of the anode inside the electrolytic cell in association with the electrolysis of the electrolyte during the electrolysis; a gas supplying step of supplying a fluid generated in the electrolytic cell during electrolysis of the electrolytic solution from the inside of the electrolytic cell to the outside of the electrolytic cell through a flow path; Equipped with In the gas supplying step, a flow path through which the fluid flows is switched in accordance with the intensity of the sound measured in the sound intensity measuring step. If the intensity of the sound measured in the sound intensity measuring step is equal to or less than a preset reference value, the fluid is supplied to a first flow path through which the fluid is supplied from inside the electrolytic cell to a first outside, and if the intensity of the sound measured in the sound intensity measuring step is greater than the preset reference value, the fluid is supplied to a second flow path through which the fluid is supplied from inside the electrolytic cell to a second outside. A method for producing fluorine gas, wherein the preset reference value is a value within a range of 10 dB or more and 60 dB or less.

[0006] [2] The method for producing fluorine gas according to [1], wherein the metal fluoride is a fluoride of at least one metal selected from the group consisting of potassium, cesium, rubidium, and lithium. [3] The method for producing fluorine gas according to [1] or [2], wherein the anode used in the electrolysis is a carbonaceous electrode made of at least one carbon material selected from diamond, diamond-like carbon, amorphous carbon, graphite, and glassy carbon. [4] The method for producing fluorine gas according to any one of [1] to [3], wherein the electrolytic cell has a structure that enables bubbles generated at an anode or a cathode used in the electrolysis to rise vertically in the electrolytic solution and reach the liquid surface of the electrolytic solution.

[0007] [5] A fluorine gas production apparatus for producing fluorine gas by electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride, an electrolytic cell containing the electrolytic solution and in which the electrolysis is carried out; a sound intensity measuring unit that measures the intensity of sound generated in the vicinity of the anode inside the electrolytic cell in association with the electrolysis of the electrolyte during the electrolysis; a flow path for transporting a fluid generated in the electrolytic cell during electrolysis of the electrolytic solution from the inside to the outside of the electrolytic cell; Equipped with the flow path includes a first flow path for sending the fluid from inside the electrolytic cell to a first outside, and a second flow path for sending the fluid from inside the electrolytic cell to a second outside, and a flow path switching unit for switching the flow path for the fluid between the first flow path and the second flow path in response to the sound intensity measured by the sound intensity measuring unit, the flow path switching unit sends the fluid from inside the electrolytic cell to the first flow path when the sound intensity measured by the sound intensity measuring unit is equal to or less than a preset reference value, and sends the fluid from inside the electrolytic cell to the second flow path when the sound intensity measured by the sound intensity measuring unit is greater than the preset reference value, A fluorine gas manufacturing apparatus, wherein the preset reference value is a value within a range of 10 dB or more and 60 dB or less. Effect of the Invention

[0008] According to the present invention, when fluorine gas is produced by electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride, clogging of pipes and valves due to mist can be suppressed. [Brief description of the drawings]

[0009] [Figure 1]FIG. 2 is a schematic diagram illustrating an example of a light scattering detector used as an average particle diameter measuring section in the fluorine gas production device according to one embodiment of the present invention. [Diagram 2] 1 is a schematic diagram illustrating an example of a fluorine gas production apparatus according to an embodiment of the present invention. [Diagram 3] FIG. 3 is a schematic diagram illustrating an example of a mist removing device used as a mist removing section in the fluorine gas production apparatus of FIG. 2. [Figure 4] FIG. 3 is a schematic diagram illustrating a first modified example of the fluorine gas production apparatus of FIG. [Diagram 5] FIG. 3 is a schematic diagram illustrating a second modified example of the fluorine gas production apparatus of FIG. [Figure 6] FIG. 3 is a schematic diagram illustrating a third modified example of the fluorine gas production apparatus of FIG. [Figure 7] FIG. 3 is a schematic diagram illustrating a fourth modified example of the fluorine gas production apparatus of FIG. [Figure 8] FIG. 3 is a schematic diagram illustrating a fifth modified example of the fluorine gas production apparatus of FIG. [Figure 9] FIG. 3 is a schematic diagram illustrating a sixth modified example of the fluorine gas production apparatus of FIG. [Figure 10] FIG. 3 is a schematic diagram illustrating a seventh modified example of the fluorine gas production apparatus of FIG. [Figure 11] FIG. 3 is a schematic diagram illustrating an eighth modified example of the fluorine gas production apparatus of FIG. [Figure 12] FIG. 13 is a schematic diagram illustrating a ninth modified example of the fluorine gas production apparatus of FIG. [Figure 13] FIG. 3 is a schematic diagram illustrating a tenth modified example of the fluorine gas production apparatus of FIG. [Figure 14] 4 is a graph showing the particle size distribution of the mist contained in the fluid generated at the anode in Reference Example 1. [Figure 15] 4 is a graph showing the correlation between the average particle size of the mist and the amount of mist generated at the anode in Reference Example 1. [Figure 16] 1 is a graph showing the relationship between the average particle size of the mist and the intensity of the popping sound generated near the anode inside the electrolytic cell in Reference Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] An embodiment of the present invention will be described below. Note that this embodiment is merely an example of the present invention, and the present invention is not limited to this embodiment. In addition, various modifications and improvements can be made to this embodiment, and such modifications and improvements can also be included in the present invention.

[0011] The present inventors have conducted extensive research into the mist that causes blockage of piping and valves in the electrolytic synthesis of fluorine gas. In the present invention, the term "mist" refers to liquid particles or solid particles that are generated together with fluorine gas in an electrolytic cell by electrolysis of an electrolyte. Specifically, the term refers to electrolyte particles, solid particles resulting from a phase change of electrolyte particles, and solid particles generated by the reaction of fluorine gas with components that constitute the electrolytic cell (metals that form the electrolytic cell, packing for the electrolytic cell, carbon electrodes, etc.).

[0012] The inventors measured the average particle size of the mist contained in the fluid generated inside the electrolytic cell during electrolysis of the electrolyte, and confirmed that the average particle size of the mist changed over time. Furthermore, as a result of intensive research, they found that there is a correlation between the average particle size of the mist and the intensity of the sound generated near the anode inside the electrolytic cell accompanying the electrolysis of the electrolyte during electrolysis, and further found that there is a correlation between the average particle size of the mist and the likelihood of blockage of the piping and valves for sending the fluid. They then found that by devising a flow path for sending the fluid generated inside the electrolytic cell according to the intensity of the sound, it is possible to suppress blockage of the piping and valves, and to reduce the frequency of interruption or stoppage of the operation for producing fluorine gas, and thus completed the present invention. One embodiment of the present invention will be described below.

[0013] The method for producing fluorine gas of the present embodiment is a method for producing fluorine gas by electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride, and includes an electrolysis step of performing electrolysis in an electrolytic cell, a sound intensity measurement step of measuring the intensity of sound generated in the vicinity of the anode inside the electrolytic cell due to the electrolysis of the electrolyte during the electrolysis, and an air supply step of supplying a fluid generated inside the electrolytic cell during the electrolysis of the electrolyte from the inside to the outside of the electrolytic cell via a flow path.

[0014] In the gas supply process, the flow path through which the fluid flows is switched depending on the sound intensity measured in the sound intensity measurement process. That is, if the sound intensity measured in the sound intensity measurement process is equal to or less than a preset reference value, the fluid is sent to a first flow path that sends the fluid from inside the electrolytic cell to a first outside, and if the sound intensity is greater than the preset reference value, the fluid is sent to a second flow path that sends the fluid from inside the electrolytic cell to a second outside. The preset reference value is a numerical value within a range of 10 dB to 60 dB.

[0015] The fluorine gas production apparatus of this embodiment is a fluorine gas production apparatus that produces fluorine gas by electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride, and is equipped with an electrolytic cell that contains the electrolyte solution and performs electrolysis, a sound intensity measuring unit that measures the intensity of sound generated in the vicinity of the anode inside the electrolytic cell due to electrolysis of the electrolyte solution during electrolysis, and a flow path that transports fluid generated inside the electrolytic cell during electrolysis of the electrolyte solution from the inside to the outside of the electrolytic cell.

[0016] The flow path includes a first flow path for sending a fluid from inside the electrolytic cell to a first outside, and a second flow path for sending a fluid from inside the electrolytic cell to a second outside. The flow path also includes a flow path switching unit for switching the flow path for the fluid between the first flow path and the second flow path depending on the sound intensity measured by the sound intensity measuring unit. The flow path switching unit is configured to send the fluid from inside the electrolytic cell to the first flow path when the sound intensity measured by the sound intensity measuring unit is equal to or lower than a preset reference value, and to send the fluid from inside the electrolytic cell to the second flow path when the sound intensity is greater than the preset reference value, the preset reference value being a numerical value within a range of 10 dB to 60 dB.

[0017] In the fluorine gas production method and fluorine gas production device of this embodiment, the flow path for flowing the fluid is switched to the first flow path or the second flow path depending on the intensity of the sound. As a result, the flow path is switched to the first flow path or the second flow path depending on the average particle diameter of the mist, and the flow path is less likely to be blocked by the mist. Therefore, the fluorine gas production method and fluorine gas production device of this embodiment can suppress the blockage of piping and valves due to the mist when producing fluorine gas by electrolyzing an electrolyte containing hydrogen fluoride and a metal fluoride. Therefore, the frequency of interruption or stop of the operation for producing fluorine gas can be reduced, and continuous operation can be easily performed. Therefore, fluorine gas can be produced economically.

[0018] The sound measured in the fluorine gas production method and fluorine gas production device of this embodiment may be, for example, a popping sound, which is considered to be generated by a reaction between the fluorine gas generated at the anode and moisture in the electrolyte. The sound intensity may be measured continuously during electrolysis, periodically at regular intervals, or irregularly as needed. Furthermore, the first flow path and the second flow path are separate flow paths, but the first outside and the second outside may be located at different positions or may be located at the same position.

[0019] Here, an example of the fluorine gas production method and fluorine gas production device of this embodiment is shown. The first flow path is a flow path that sends a fluid from the inside of the electrolytic cell to a fluorine gas selection section that selects and extracts fluorine gas from the fluid via a mist removal section that removes mist from the fluid. The second flow path is a flow path that sends a fluid from the inside of the electrolytic cell to the fluorine gas selection section without passing through the mist removal section. That is, when the intensity of the sound is equal to or less than a preset reference value, the fluid is sent to the mist removal section provided in the first flow path, and when it is greater than the preset reference value, the fluid is not sent to the mist removal section. In this example, the fluorine gas selection section corresponds to the first outside and the second outside, and the first outside and the second outside are the same location, but the first outside and the second outside may be different locations.

[0020] The second flow path has a clogging suppression mechanism that suppresses clogging of the second flow path by mist. The clogging suppression mechanism is not particularly limited as long as it can suppress clogging of the second flow path by mist, and examples thereof include the following. That is, examples include a large diameter pipe, an inclined pipe, a rotating screw, and an airflow generating device, and these may be used in combination. Specifically, by configuring at least a portion of the second flow path with a pipe having a larger diameter than the first flow path, it is possible to suppress clogging of the second flow path by the mist. Also, by configuring at least a portion of the second flow path with a pipe that is inclined with respect to the horizontal direction and extends in a downward direction from the upstream side to the downstream side, it is possible to suppress clogging of the second flow path by the mist.

[0021] Furthermore, by installing a rotating screw inside the second flow path that sends the mist accumulated inside the second flow path to the upstream or downstream side, it is possible to suppress clogging of the second flow path due to the mist. Furthermore, by providing an airflow generating device in the second flow path that generates an airflow to increase the flow speed of the fluid flowing through the second flow path, it is possible to suppress clogging of the second flow path due to the mist. Note that a mist removal unit different from the mist removal unit provided in the first flow path may be provided in the second flow path as a clogging suppression mechanism.

[0022] The first flow path is less likely to be clogged by mist because the mist is removed from the fluid by the mist removal unit, and the second flow path is less likely to be clogged by mist because a clogging suppression mechanism is provided. Therefore, the fluorine gas production method and fluorine gas production device of this embodiment can suppress clogging of pipes and valves due to mist when producing fluorine gas by electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride. Note that even if the mist removal unit and clogging suppression mechanism are not provided, the effect of suppressing clogging of pipes and valves due to mist can be achieved simply by switching the flow path through which the fluid flows to another flow path (the first flow path or the second flow path), but the above effect is superior when a mist removal unit and a clogging suppression mechanism are provided.

[0023] The fluorine gas production method and fluorine gas production apparatus of this embodiment will be described in further detail below. [Electrolytic cell] There is no particular limitation on the type of electrolytic cell, and any electrolytic cell can be used as long as it can generate fluorine gas by electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride. Usually, the inside of an electrolytic cell is partitioned by a partition member such as a partition wall into an anode chamber in which an anode is disposed and a cathode chamber in which a cathode is disposed, so that fluorine gas generated at the anode and hydrogen gas generated at the cathode do not mix with each other.

[0024] As the anode, for example, a carbonaceous electrode made of a carbon material such as diamond, diamond-like carbon, amorphous carbon, graphite, glassy carbon, or amorphous carbon can be used. In addition to the above carbon materials, for example, a metal electrode made of a metal such as nickel or Monel (trademark) can also be used as the anode. As the cathode, for example, a metal electrode made of a metal such as iron, copper, nickel, or Monel (trademark) can be used.

[0025] The electrolytic solution contains hydrogen fluoride and a metal fluoride, and the type of the metal fluoride is not particularly limited, but is preferably a fluoride of at least one metal selected from potassium, cesium, rubidium, and lithium. If the electrolytic solution contains cesium or rubidium, the specific gravity of the electrolytic solution increases, thereby suppressing the amount of mist generated during electrolysis.

[0026] As the electrolyte, for example, a mixed molten salt of hydrogen fluoride (HF) and potassium fluoride (KF) can be used. The molar ratio of hydrogen fluoride to potassium fluoride in the mixed molten salt of hydrogen fluoride and potassium fluoride can be, for example, hydrogen fluoride:potassium fluoride=1.5 to 2.5:1. When the ratio of hydrogen fluoride to potassium fluoride is 2:1, KF·2HF is a representative electrolyte, and the melting point of this mixed molten salt is about 72°C. Since this electrolyte is corrosive, it is preferable that the parts in contact with the electrolyte, such as the inner surface of the electrolytic cell, are made of metals such as iron, nickel, Monel (trademark), etc.

[0027] During electrolysis of the electrolyte, a direct current is applied to the anode and the cathode, and a gas containing fluorine gas is generated at the anode, and a gas containing hydrogen gas is generated at the cathode. In addition, since hydrogen fluoride in the electrolyte has a vapor pressure, hydrogen fluoride is entrained in the gas generated at the anode and the cathode. Furthermore, in the production of fluorine gas by electrolysis of the electrolyte, the gas generated by electrolysis contains a mist of the electrolyte. Therefore, the gas phase portion of the electrolytic cell is composed of the gas generated by electrolysis, hydrogen fluoride, and the mist of the electrolyte. Therefore, what is sent from the inside of the electrolytic cell to the outside is composed of the gas generated by electrolysis, hydrogen fluoride, and the mist of the electrolyte, and in the present invention, this is referred to as a "fluid."

[0028] Since hydrogen fluoride in the electrolytic solution is consumed as the electrolysis proceeds, a pipe for continuously or intermittently supplying hydrogen fluoride to the electrolytic cell for replenishment may be connected to the electrolytic cell. Hydrogen fluoride may be supplied to the cathode chamber side or the anode chamber side of the electrolytic cell. The main reasons why mist is generated during electrolysis of electrolyte are as follows. The temperature of the electrolyte during electrolysis is adjusted to, for example, 80 to 100°C. Since the melting point of KF·2HF is 71.7°C, the electrolyte is in a liquid state when adjusted to the above temperature. Gas bubbles generated at both electrodes of the electrolytic cell rise in the electrolyte and burst at the liquid surface of the electrolyte. At this time, part of the electrolyte is released into the gas phase.

[0029] Because the temperature of the gas phase is lower than the melting point of the electrolyte, the released electrolyte changes phase to a very fine powder-like state. This powder is thought to be a mixture of potassium fluoride and hydrogen fluoride, KF·nHF. This powder becomes mist along with the other gases generated, forming the fluid generated in the electrolytic cell. This mist is difficult to effectively remove by ordinary measures such as installing filters, due to its sticky nature.

[0030] In addition, although the amount generated is small, a fine powder of an organic compound may be generated as a mist due to a reaction between the carbonaceous electrode, which is the anode, and the fluorine gas generated by electrolysis. In detail, a contact resistance often occurs in the part that supplies the current to the carbonaceous electrode, and the temperature may become higher than that of the electrolyte due to Joule heat. Therefore, a soot-like organic compound CFx may be generated as a mist due to a reaction between the carbon that forms the carbonaceous electrode and the fluorine gas.

[0031] In addition, the electrolytic cell preferably has a structure in which bubbles generated at the anode or cathode used in electrolysis can rise vertically in the electrolyte and reach the liquid surface of the electrolyte. If the structure makes it difficult for bubbles to rise vertically in the electrolyte and rise in a direction inclined relative to the vertical direction, multiple bubbles tend to gather together and generate large bubbles. As a result, large bubbles reach the liquid surface of the electrolyte and burst, so the amount of mist is likely to increase. If the structure allows bubbles to rise vertically in the electrolyte and reach the liquid surface of the electrolyte, small bubbles reach the liquid surface of the electrolyte and burst, so the amount of mist is likely to decrease.

[0032] [Average particle diameter measuring section] The fluorine gas production apparatus of this embodiment may be provided with an average particle diameter measuring unit that measures the average particle diameter of the mist contained in the fluid, and this average particle diameter measuring unit may be composed of a light scattering detector that measures the average particle diameter by a light scattering method. The light scattering detector is preferable as the average particle diameter measuring unit because it can measure the average particle diameter of the mist in the fluid flowing through the flow path while the fluorine gas production apparatus is continuously operated.

[0033] An example of a light scattering detector will be described with reference to Fig. 1. The light scattering detector in Fig. 1 is a light scattering detector that can be used as an average particle size measuring unit in a fluorine gas production apparatus of this embodiment (for example, the fluorine gas production apparatus in Figs. 2 and 4 to 13 described later). That is, it is a light scattering detector that measures the average particle size of mist contained in a fluid generated inside an electrolytic cell of a fluorine gas production apparatus when fluorine gas is produced by electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride inside the electrolytic cell. The light scattering detector may be connected to the fluorine gas production apparatus and the fluid may be sent from inside the electrolytic cell to the light scattering detector to measure the average particle diameter of the mist, or the light scattering detector may not be connected to the fluorine gas production apparatus, and the fluid may be taken from inside the electrolytic cell and introduced into the light scattering detector to measure the average particle diameter of the mist.

[0034] The light scattering detector in Fig. 1 includes a sample chamber 1 that contains a fluid F, a light source 2 that irradiates the fluid F in the sample chamber 1 with light scattering measurement light L, a scattered light detection unit 3 that detects scattered light S generated when the light scattering measurement light L is scattered by mist M in the fluid F, a transparent window 4A that is installed in the sample chamber 1 and comes into contact with the fluid F to transmit the light scattering measurement light L, and a transparent window 4B that is installed in the sample chamber 1 and comes into contact with the fluid F to transmit the scattered light S. The transparent windows 4A and 4B are made of at least one material selected from diamond, calcium fluoride (CaF2), potassium fluoride (KF), silver fluoride (AgF), barium fluoride (BaF2), and potassium bromide (KBr).

[0035] The light scattering measurement light L (e.g., laser light) emitted from the light source 2 passes through the convergent lens 6 and the transparent window 4A of the sample chamber 1, enters the sample chamber 1, and is irradiated onto the fluid F contained in the sample chamber 1. At this time, if a light-reflecting substance such as mist M is present in the fluid F, the light scattering measurement light L is reflected and scattered. A part of the scattered light S generated by the light scattering measurement light L being scattered by the mist M passes through the transparent window 4B of the sample chamber 1 and is taken out of the sample chamber 1, and enters the scattered light detection unit 3 via the condenser lens 7 and the aperture 8. At this time, the average particle diameter of the mist M can be known from the information obtained from the scattered light S. The average particle diameter obtained here is the number-average particle diameter. For example, an aerosol spectrometer welas (registered trademark) digital 2000 manufactured by PALAS can be used as the scattered light detection unit 3.

[0036] The transparent windows 4A, 4B come into contact with the fluid F, which contains highly reactive fluorine gas, so the transparent windows 4A, 4B must be made of a material that is resistant to corrosion by fluorine gas. Examples of materials for forming the transparent windows 4A, 4B include at least one selected from diamond, calcium fluoride, potassium fluoride, silver fluoride, barium fluoride, and potassium bromide. If the transparent windows 4A, 4B are made of the above materials, deterioration due to contact with the fluid F can be suppressed.

[0037] Also, a film made of the above-mentioned material may be coated on the surface of glass such as quartz, and used as the transparent windows 4A, 4B. Since the portion that comes into contact with the fluid F is coated with a film made of the above-mentioned material, deterioration due to contact with the fluid F can be suppressed while keeping costs down. The transparent windows 4A, 4B may be a laminate in which the surface that comes into contact with the fluid F is made of the above-mentioned material, and the other portions are made of ordinary glass such as quartz. The material of the parts of the light scattering detector other than the transparent windows 4A and 4B is not particularly limited as long as it is a material that is resistant to corrosion by fluorine gas, but it is preferable to use a metallic material such as Monel (trademark), which is a copper-nickel alloy, Hastelloy (trademark), stainless steel, etc.

[0038] [Average particle size of mist and intensity of sound generated near the anode inside the electrolytic cell due to electrolysis of electrolyte during electrolysis] The present inventors measured the average particle size of the mist generated during the production of fluorine gas by electrolysis of an electrolyte using a light scattering detector. An example of the results will be described. After replacing the anode of the fluorine gas production device with a new anode or filling the electrolytic cell with new electrolyte, electrolysis was started, and the average particle size of the mist in the fluid generated at the anode for a certain period of time immediately after the start of electrolysis was measured. As a result, the average particle size of the mist was 0.5 to 2.0 μm. After that, the electrolysis was continued and the electrolysis began to stabilize after a sufficient amount of time had passed, and the average particle size of the mist in the fluid during this stable electrolysis was about 0.2 μm.

[0039] In this way, mist with a relatively large particle size is generated during the period from immediately after the start of electrolysis until stable electrolysis is reached. When a fluid containing large mist immediately after the start of electrolysis flows through a pipe or valve, the mist is likely to adhere to the inner surface of the pipe or valve, causing blockage of the pipe or valve. In contrast, during stable electrolysis, the particle size of the mist generated is relatively small. Such small mist is less likely to settle or accumulate in the fluid, and can flow stably through pipes and valves. Therefore, during stable electrolysis, the fluid consisting of the mist and the gas generated at the electrodes is relatively unlikely to cause blockage of pipes or valves. The time from immediately after the start of electrolysis until stable electrolysis is reached is usually 25 hours or more and 200 hours or less. Also, from immediately after the start of electrolysis until stable electrolysis is reached, approximately 40 kAh or more of current is required per 1000 L of electrolyte.

[0040] The inventors have also found that there is a close relationship between the average particle size of the mist and the intensity of the sound. Usually, the intensity of the sound is large at the start of electrolysis, and is greater than 30 dB. The average particle size of the mist at this time is greater than 0.4 μm. Thereafter, as electrolysis continues, the intensity of the sound decreases, and when it becomes 30 dB or less, the average particle size of the mist becomes 0.4 μm or less.

[0041] In this way, since there is a correlation between the average particle size of the mist and the sound intensity, the sound intensity can be measured instead of the average particle size of the mist during electrolysis, and the measurement result can be used to switch the flow path. In other words, if the sound intensity is measured at a predetermined timing during electrolysis, the flow path through which the fluid generated by electrolysis flows can be appropriately switched at the predetermined timing according to the measurement result.

[0042] Based on these findings, the present inventors have invented the above-mentioned fluorine gas production method and fluorine gas production device having a structure capable of switching a flow path for a fluid according to the intensity of the sound. The fluorine gas production device of this embodiment has a first flow path and a second flow path, and may be configured to select one of the two flow paths to be used for transporting the fluid by using a flow path switching unit (e.g., a switching valve).

[0043] Alternatively, the fluorine gas production apparatus of this embodiment may have two flow paths and a moving and replacing mechanism for moving and replacing the electrolytic cell, and may be configured to select one of the two flow paths to be used for transporting a fluid, and to move and connect the electrolytic cell to the vicinity of that flow path, thereby switching the flow path. As described above, since the first flow path and the second flow path are provided, even while one flow path is blocked for cleaning, the other flow path can be opened and the fluorine gas production apparatus can be operated continuously.

[0044] According to the study by the inventors, a mist with a relatively large average particle size is generated immediately after the start of electrolysis until stable electrolysis is reached, and at this time, the fluid may be sent to the second flow path having a clogging suppression mechanism. As time passes and stable electrolysis is reached, a mist with a relatively small average particle size is generated, and at this time, the flow path may be switched to send the fluid to the first flow path having a mist removal unit.

[0045] The flow path is switched according to the intensity of the sound measured, but the flow path is switched based on a preset reference value. The appropriate reference value for the average particle size of the mist generated at the anode varies depending on the device, but is, for example, 0.1 μm to 1.0 μm, preferably 0.2 μm to 0.8 μm, and more preferably 0.4 μm. Therefore, based on the correlation between the average particle size of the mist and the sound intensity, an appropriate standard value for the sound intensity is 10 dB to 60 dB, preferably 20 dB to 40 dB, and more preferably 30 dB. If the sound intensity is greater than the standard value, the fluid can be sent to the second flow path, and if it is equal to or less than the standard value, the fluid can be sent to the first flow path.

[0046] The method for measuring the sound intensity is not particularly limited, but for example, the sound intensity can be measured by detecting the sound with a sound detection device such as a sound sensor or a sound collecting microphone and converting it into an electric signal. The location of the sound detection device is not particularly limited, and may be inside or outside the electrolytic cell, for example, outside the top plate (upper lid) of the electrolytic cell. As an example, the sound detection device may be installed at a position 5 to 20 cm above the top plate of the electrolytic cell. The fluid (mainly hydrogen gas) generated at the cathode contains, for example, 20 to 50 μg of powder per unit volume (1 liter) (calculated assuming that the specific gravity of the mist is 1.0 g / mL), and the average particle size of this powder is approximately 0.1 μm with a distribution of ±0.05 μm.

[0047] In the fluid generated at the cathode, no significant difference was observed in the particle size distribution of the generated powder due to the sound intensity. The mist contained in the fluid generated at the cathode has a smaller average particle size than the mist contained in the fluid generated at the anode, so it is less likely to cause blockage of pipes or valves than the mist contained in the fluid generated at the anode. Therefore, the mist contained in the fluid generated at the cathode can be removed from the fluid using an appropriate removal method.

[0048] An example of the fluorine gas production apparatus of this embodiment will be described in detail with reference to Fig. 2. The fluorine gas production apparatus in Fig. 2 is an example equipped with two electrolytic cells, but the number of electrolytic cells may be one or three or more, for example, 10 to 15. The fluorine gas production apparatus shown in FIG. 2 comprises electrolytic cells 11, 11 which contain electrolytic solution 10 and in which electrolysis is carried out, an anode 13 which is disposed inside the electrolytic cell 11 and immersed in the electrolytic solution 10, and a cathode 15 which is disposed inside the electrolytic cell 11 and immersed in the electrolytic solution 10 and opposed to the anode 13.

[0049] The interior of the electrolytic cell 11 is divided into an anode chamber 22 and a cathode chamber 24 by a partition wall 17 that extends vertically downward from the ceiling surface inside the electrolytic cell 11 and has a lower end immersed in the electrolyte 10. An anode 13 is disposed in the anode chamber 22, and a cathode 15 is disposed in the cathode chamber 24. The space above the liquid level of the electrolyte 10 is separated by the partition wall 17 into the space in the anode chamber 22 and the space in the cathode chamber 24, and a portion of the electrolyte 10 above the lower end of the partition wall 17 is separated by the partition wall 17, but a portion of the electrolyte 10 below the lower end of the partition wall 17 is not directly separated by the partition wall 17 and is continuous.

[0050] The fluorine gas production apparatus shown in FIG. 2 also includes a sound intensity measuring unit 37 that measures the intensity of sound generated near the anode 13 inside the electrolytic cell 11 due to the electrolysis of the electrolyte 10 during electrolysis, a first average particle size measuring unit 31 that measures the average particle size of mist contained in the fluid generated inside the electrolytic cell 11 during the electrolysis of the electrolyte 10, a first mist removal unit 32 that removes the mist from the fluid, a fluorine gas selection unit (not shown) that selects and extracts fluorine gas from the fluid, and a flow path that sends the fluid from inside the electrolytic cell 11 to the fluorine gas selection unit.

[0051] Furthermore, this flow path has a first flow path that sends the fluid from inside the electrolytic cell 11 to the fluorine gas selector via the first mist removal section 32, and a second flow path that sends the fluid from inside the electrolytic cell 11 to the fluorine gas selector without passing through the first mist removal section 32. This flow path also has a flow path switching section that switches the flow path for the fluid to the first flow path or the second flow path depending on the sound intensity measured by the sound intensity measuring section 37. That is, the flow path switching section is provided midway along the flow path extending from the electrolytic cell 11, and the flow path for the fluid to flow can be changed by the flow path switching section.

[0052] This flow path switching unit sends the fluid from inside the electrolytic cell 11 to the first flow path when the sound intensity measured by the sound intensity measuring unit 37 is equal to or lower than a preset reference value, and sends the fluid from inside the electrolytic cell 11 to the second flow path when the sound intensity is greater than the preset reference value. The second flow path has a clogging suppression mechanism that suppresses clogging of the second flow path due to mist.

[0053] In other words, when the sound intensity is below a reference value, the fluid is sent to a first flow path which connects the electrolytic cell 11 and the fluorine gas selection section and is provided with a first mist removal section 32, and when the sound intensity is greater than the reference value, the fluid is sent to a second flow path which connects the electrolytic cell 11 and the fluorine gas selection section and is provided with a blockage suppression mechanism. As the sound intensity measurement unit 37, for example, a sound sensor can be used.

[0054] For example, a mist removal device capable of removing mist having an average particle diameter of 0.4 μm or less from the fluid is used as the first mist removal section 32. The type of mist removal device, i.e., the method of removing the mist, is not particularly limited, but since the average particle diameter of the mist is small, for example, an electric dust collector, a venturi scrubber, or a filter can be used as the mist removal device.

[0055] Among the above mist removal devices, it is preferable to use the mist removal device shown in Fig. 3. The mist removal device shown in Fig. 3 is a scrubber type mist removal device that uses liquid hydrogen fluoride as a circulating liquid. The mist removal device shown in Fig. 3 can efficiently remove mist with an average particle size of 0.4 µm or less from a fluid. In addition, while liquid hydrogen fluoride is used as the circulating liquid, it is preferable to cool the circulating liquid in order to reduce the concentration of hydrogen fluoride in the fluorine gas, and therefore the concentration of hydrogen fluoride in the fluorine gas can be adjusted by controlling the cooling temperature.

[0056] The fluorine gas production apparatus shown in Fig. 2 will be described in further detail. A first pipe 41, which sends the fluid (hereinafter sometimes referred to as "anode gas") generated in the anode chamber 22 of the electrolytic cell 11 to the outside, communicates with the electrolytic cell 11 and a fourth pipe 44, and the anode gas sent out from the two electrolytic cells 11, 11 is sent by the first pipe 41 to the fourth pipe 44 and mixed therein. The main component of the anode gas is fluorine gas, and the secondary components are mist, hydrogen fluoride, carbon tetrafluoride, oxygen gas, and water.

[0057] The fourth pipe 44 is connected to the first mist removal section 32, and the anode gas is sent to the first mist removal section 32 by the fourth pipe 44, so that the mist and hydrogen fluoride in the anode gas are removed from the anode gas by the first mist removal section 32. The anode gas from which the mist and hydrogen fluoride have been removed is sent from the first mist removal section 32 to a fluorine gas selection section (not shown) by a sixth pipe 46 connected to the first mist removal section 32. Then, the fluorine gas is selected from the anode gas and extracted by the fluorine gas selection section.

[0058] An eighth pipe 48 is connected to the first mist removal section 32, and liquid hydrogen fluoride, which is a circulating fluid, is supplied to the first mist removal section 32 by the eighth pipe 48. Furthermore, a ninth pipe 49 is connected to the first mist removal section 32. The ninth pipe 49 is connected to the electrolytic cells 11, 11 via the third pipe 43, and the circulating fluid (liquid hydrogen fluoride) that is used to remove mist in the first mist removal section 32 and contains mist is returned from the first mist removal section 32 to the electrolytic cells 11, 11.

[0059] The cathode chamber 24 of the electrolytic cell 11 is similar to the anode chamber 22. That is, a second pipe 42 that sends a fluid generated in the cathode chamber 24 of the electrolytic cell 11 (hereinafter, sometimes referred to as "cathode gas") to the outside communicates between the electrolytic cell 11 and a fifth pipe 45, and the cathode gas sent out from the two electrolytic cells 11, 11 is sent to the fifth pipe 45 by the second pipe 42 and mixed therein. The main component of the cathode gas is hydrogen gas, and the secondary components are mist, hydrogen fluoride, and water.

[0060] Since the cathode gas contains fine mist and 5 to 10% by volume of hydrogen fluoride, it is not preferable to discharge the cathode gas directly into the atmosphere. Therefore, the fifth pipe 45 is connected to the second mist removal section 33, and the cathode gas is sent to the second mist removal section 33 by the fifth pipe 45, and the mist and hydrogen fluoride in the cathode gas are removed from the cathode gas by the second mist removal section 33. The cathode gas from which the mist and hydrogen fluoride have been removed is discharged from the second mist removal section 33 into the atmosphere by the seventh pipe 47 connected to the second mist removal section 33. The type of the second mist removal section 33, that is, the method of removing the mist, is not particularly limited, but a scrubber-type mist removal device using an alkaline aqueous solution as a circulating liquid can be used.

[0061] The pipe diameter and installation direction (meaning the direction in which the pipes extend, e.g., vertical or horizontal) of the first pipe 41, the second pipe 42, the fourth pipe 44, and the fifth pipe 45 are not particularly limited, but it is preferable that the first pipe 41 and the second pipe 42 are installed so as to extend vertically from the electrolytic cell 11, and have a pipe diameter such that the flow velocity of the fluid flowing through the first pipe 41 and the second pipe 42 is 30 cm / sec or less under standard conditions. In this way, even if mist contained in the fluid falls under its own weight, the mist settles inside the electrolytic cell 11, and therefore the inside of the first pipe 41 and the second pipe 42 are less likely to be clogged by powder. In addition, it is preferable that the fourth pipe 44 and the fifth pipe 45 are installed to extend horizontally and have a pipe diameter such that the flow speed of the fluid flowing through the fourth pipe 44 and the fifth pipe 45 is approximately 1 to 10 times faster than that of the first pipe 41 and the second pipe 42.

[0062] Further, a second bypass pipe 52 for sending the anode gas to the outside of the electrolytic cell 11 is provided separately from the first pipe 41. That is, the second bypass pipe 52 communicates the electrolytic cell 11 with the first bypass pipe 51, and the anode gas sent from the two electrolytic cells 11, 11 is sent to the first bypass pipe 51 by the second bypass pipe 52 and mixed therewith. Furthermore, the anode gas is sent to a fluorine gas selection section (not shown) by the first bypass pipe 51. Then, the fluorine gas is selected from the anode gas and taken out by the fluorine gas selection section. Note that the fluorine gas selection section connected to the first bypass pipe 51 and the fluorine gas selection section connected to the sixth pipe 46 may be the same or different.

[0063] The pipe diameter and installation direction of the second bypass pipe 52 are not particularly limited, but it is preferable that the second bypass pipe 52 is installed to extend vertically from the electrolytic cell 11 and that the pipe diameter is such that the flow velocity of the fluid flowing through the second bypass pipe 52 is 30 cm / sec or less under standard conditions.

[0064] The first bypass pipe 51 is installed so as to extend along the horizontal direction. The first bypass pipe 51 has a larger pipe diameter than the fourth pipe 44, and the pipe diameter of the first bypass pipe 51 is set to a size such that clogging of the first bypass pipe 51 due to accumulation of powder is unlikely to occur. Since the first bypass pipe 51 has a larger pipe diameter than the fourth pipe 44, a clogging prevention mechanism is formed. The pipe diameter of the first bypass pipe 51 is preferably more than 1.0 and not more than 3.2 times that of the fourth pipe 44, and more preferably 1.05 to 1.5 times. In other words, the flow path cross-sectional area of ​​the first bypass pipe 51 is preferably 10 times or less that of the fourth pipe 44.

[0065] As can be seen from the above description, the first flow path is configured by the first pipe 41 and the fourth pipe 44, and the second flow path is configured by the first bypass pipe 51 and the second bypass pipe 52. A clogging suppression mechanism is provided in the first bypass pipe 51 constituting the second flow path.

[0066] Next, the flow path switching unit will be described. A first pipe valve 61 is provided in each of the first pipes 41. By switching the first pipe valve 61 between an open state and a closed state, it is possible to control whether or not anode gas is sent from the electrolytic cell 11 to the first mist removal unit 32. A bypass valve 62 is provided in each of the second bypass pipes 52. By switching the bypass valve 62 between an open state and a closed state, it is possible to control whether or not anode gas is sent from the electrolytic cell 11 to the first bypass pipe 51. Furthermore, a sound intensity measuring unit 37 is installed in the electrolytic cell 11, which makes it possible to measure the intensity of sound generated in the vicinity of the anode 13 inside the electrolytic cell 11 in association with the electrolysis of the electrolyte 10 during electrolysis.

[0067] Furthermore, a first average particle diameter measuring unit 31 is installed between the electrolytic cell 11 and the first mist removal unit 32, more specifically, in the middle of the fourth pipe 44 and downstream of the connecting part with the first pipe 41. The first average particle diameter measuring unit 31 measures the average particle diameter of the mist contained in the anode gas flowing through the fourth pipe 44. Moreover, by analyzing the fluorine gas and nitrogen gas contained in the anode gas after measuring the average particle diameter of the mist, the current efficiency in the production of fluorine gas can be measured.

[0068] A similar second average particle diameter measuring unit 34 is also provided in the middle of the first bypass piping 51 and downstream of the connecting portion with the second bypass piping 52, and the second average particle diameter measuring unit 34 measures the average particle diameter of the mist contained in the anode gas flowing through the first bypass piping 51. However, the fluorine gas production apparatus shown in FIG. 2 does not necessarily have to include the first average particle diameter measuring unit 31 and the second average particle diameter measuring unit 34.

[0069] The sound intensity measuring unit 37 measures the intensity of sound generated near the anode 13 inside the electrolytic cell 11 in association with the electrolysis of the electrolyte 10 during electrolysis, and if the measurement result is greater than a preset reference value, the bypass valve 62 is opened to send the anode gas from the electrolytic cell 11 to the first bypass piping 51, and the first piping valve 61 is closed to prevent the anode gas from being sent to the fourth piping 44 and the first mist removal unit 32. In other words, the anode gas is sent to the second flow path.

[0070] On the other hand, if the measurement result is equal to or lower than the preset reference value, the first piping valve 61 is opened to send the anode gas to the fourth piping 44 and the first mist removal unit 32, and the bypass valve 62 is closed to prevent the anode gas from being sent from the electrolytic cell 11 to the first bypass piping 51. In other words, the anode gas is sent to the first flow path. As can be seen from the above description, the first piping valve 61 and the bypass valve 62 constitute the flow path switching unit.

[0071] As described above, by operating the fluorine gas production apparatus while switching the flow path according to the intensity of the sound, it is possible to perform smooth continuous operation while suppressing blockage of pipes and valves due to mist. Therefore, the fluorine gas production apparatus shown in Fig. 2 can produce fluorine gas economically.

[0072] For example, a plurality of pipes each equipped with a filter may be prepared as the mist removing section, and electrolysis may be performed by switching between the pipes as appropriate and replacing the filters. Furthermore, it is preferable to judge the period when the filter should be replaced frequently and the period when the filter does not need to be replaced frequently based on the sound intensity measurement. Then, by appropriately adjusting the frequency of switching the pipes through which the fluid flows based on the judgment, the fluorine gas production apparatus can be operated efficiently and continuously.

[0073] Next, a modified example of the fluorine gas production apparatus shown in FIG. 2 will be described. [First Modification] The first modified example will be described with reference to Fig. 4. In the fluorine gas production apparatus shown in Fig. 2, the second bypass pipe 52 connects the electrolytic cell 11 and the first bypass pipe 51, whereas in the fluorine gas production apparatus of the first modified example shown in Fig. 4, the second bypass pipe 52 connects the first pipe 41 and the first bypass pipe 51. The configuration of the fluorine gas production apparatus of the first modified example is almost the same as that of the fluorine gas production apparatus of Fig. 2 except for the above points, so a description of the similar parts will be omitted.

[0074] [Second Modification] The second modified example will be described with reference to Fig. 5. The fluorine gas production apparatus of the second modified example shown in Fig. 5 is an example including one electrolytic cell 11. The first average particle size measuring unit 31 is provided in the first pipe 41, not in the fourth pipe 44, and is provided upstream of the first pipe valve 61. In addition, the second bypass pipe 52 is not provided, and the first bypass pipe 51 is directly connected to the electrolytic cell 11 without passing through the second bypass pipe 52.

[0075] The first bypass pipe 51 has a larger diameter than the fourth pipe 44, and therefore functions as a clogging prevention mechanism. Furthermore, for example, by providing a space for mist accumulation at the downstream end of the first bypass pipe 51, the effect of clogging prevention can be further increased. Examples of the space for mist accumulation include a space in which the downstream end portion of the first bypass pipe 51 is formed with a larger pipe diameter (for example, four times or more the pipe diameter of the central portion in the installation direction) than the central portion in the installation direction, and a space in which the downstream end portion of the first bypass pipe 51 is formed in a shape like a container, and the space for mist accumulation can prevent clogging of the first bypass pipe 51. This is aimed at the effect of preventing clogging due to the large cross-sectional area of ​​the flow path and the effect of preventing clogging by utilizing the gravitational fall of mist due to the decrease in the linear velocity of the gas flow. Furthermore, the bypass valve 62 is provided in a third bypass pipe 53 that connects the first bypass pipe 51 with a fluorine gas selection section (not shown). The configuration of the fluorine gas production apparatus of the second modified example is almost the same as that of the fluorine gas production apparatus of Fig. 2 except for the above points, so a description of the similar parts will be omitted.

[0076] [Third Modification] The third modified example will be described with reference to Fig. 6. In the fluorine gas production apparatus of the third modified example, a first average particle diameter measuring unit 31 is provided in the electrolytic cell 11, and the anode gas inside the electrolytic cell 11 is directly introduced into the first average particle diameter measuring unit 31 to measure the average particle diameter of the mist. The fluorine gas production apparatus of the third modified example does not have a second average particle diameter measuring unit 34. The configuration of the fluorine gas production apparatus of the third modified example is substantially the same as that of the fluorine gas production apparatus of the second modified example except for the above points, so a description of the similar parts will be omitted.

[0077] [Fourth Modification] The fourth modified example will be described with reference to FIG. 7. The fluorine gas production apparatus of the fourth modified example is an example in which the clogging suppression mechanism is different from that of the second modified example shown in FIG. 5. In the fluorine gas production apparatus of the second modified example, the first bypass pipe 51 is installed so as to extend along the horizontal direction, but in the fluorine gas production apparatus of the fourth modified example, the first bypass pipe 51 is inclined with respect to the horizontal direction and extends in a downward direction from the upstream side to the downstream side. This inclination suppresses the accumulation of powder inside the first bypass pipe 51. The greater the inclination, the greater the effect of suppressing the accumulation of powder. The inclination angle of the first bypass piping 51 is preferably 30 degrees or more, and more preferably 40 degrees or more and 60 degrees or less, with the depression angle from the horizontal plane being in the range of less than 90 degrees. If clogging of the first bypass piping 51 is likely to occur, by hammering the inclined first bypass piping 51, the deposits inside the first bypass piping 51 can be easily moved, thereby preventing clogging. The configuration of the fluorine gas production apparatus of the fourth modified example is substantially the same as that of the fluorine gas production apparatus of the second modified example except for the above points, so a description of the similar parts will be omitted.

[0078] [Fifth Modification] The fifth modification will be described with reference to FIG. 8. The fifth modification is an example in which the clogging suppression mechanism is different from that of the third modification shown in FIG. 6. In the third modification, the first bypass pipe 51 is installed to extend along the horizontal direction, but in the fifth modification, the first bypass pipe 51 is inclined with respect to the horizontal direction and extends in a downward direction from the upstream side to the downstream side. This inclination suppresses the accumulation of powder inside the first bypass pipe 51. The preferred inclination angle of the first bypass pipe 51 is the same as in the fourth modification. The configuration of the fifth modification is almost the same as that of the third modification except for the above points, so a description of the similar parts will be omitted.

[0079] [Sixth Modification] The sixth modified example will be described with reference to Fig. 9. The fluorine gas production apparatus of the sixth modified example is an example in which the structure of the electrolytic cell 11 is different from that of the second modified example shown in Fig. 5. The electrolytic cell 11 has one anode 13 and two cathodes 15, 15, and is partitioned into one anode chamber 22 and one cathode chamber 24 by a cylindrical partition wall 17 surrounding the one anode 13. The anode chamber 22 is formed to extend above the upper surface of the electrolytic cell 11, and the first bypass pipe 51 is connected to the upper end portion of the anode chamber 22 of the electrolytic cell 11. The configuration of the fluorine gas production apparatus of the sixth modified example is substantially the same as that of the fluorine gas production apparatus of the second modified example except for the above points, and therefore a description of the similar parts will be omitted.

[0080] [Seventh Modification] The seventh modification will be described with reference to Fig. 10. The seventh modification is an example in which the structure of the first bypass pipe 51 is different from that of the sixth modification shown in Fig. 9. That is, in the seventh modification, the first bypass pipe 51 is inclined with respect to the horizontal direction and extends in a downward direction from the upstream side to the downstream side, similar to the fourth and fifth modifications. The preferred angle of inclination of the first bypass pipe 51 is the same as in the fourth modification. The configuration of the seventh modification is almost the same as that of the sixth modification, except for the above points, and therefore a description of the similar parts will be omitted.

[0081] [Eighth Modification] The eighth modified example will be described with reference to Fig. 11. The fluorine gas production apparatus of the eighth modified example is an example in which the clogging suppression mechanism is different from that of the second modified example shown in Fig. 5. In the fluorine gas production apparatus of the eighth modified example, a rotating screw 71 constituting the clogging suppression mechanism is installed inside the first bypass pipe 51. The rotating screw 71 is installed with its rotation axis parallel to the longitudinal direction of the first bypass pipe 51. Then, by rotating the rotary screw 71 with the motor 72, the mist accumulated inside the first bypass pipe 51 can be sent to the upstream or downstream side. This prevents the powder from accumulating inside the first bypass pipe 51. The configuration of the fluorine gas production apparatus of the eighth modified example is almost the same as that of the fluorine gas production apparatus of the second modified example except for the above points, so a description of the similar parts will be omitted.

[0082] [Ninth Modification] The ninth modified example will be described with reference to Fig. 12. The fluorine gas production apparatus of the ninth modified example is an example in which the clogging suppression mechanism is different from that of the second modified example shown in Fig. 5. In the fluorine gas production apparatus of the ninth modified example, an airflow generator 73 constituting the clogging suppression mechanism is installed in the first bypass pipe 51. The airflow generator 73 sends an airflow (e.g., an airflow of nitrogen gas) from the upstream side to the downstream side of the first bypass pipe 51, and increases the flow rate of the anode gas flowing inside the first bypass pipe 51. This suppresses the accumulation of powder inside the first bypass pipe 51.

[0083] At this time, the preferred flow velocity of the anode gas flowing through the first bypass piping 51 is 1 m / sec or more and 10 m / sec or less. It is possible to set the flow velocity to more than 10 m / sec, but in that case, the pressure loss due to piping resistance in the first bypass piping 51 increases, and the pressure in the anode chamber 22 of the electrolytic cell 11 increases. It is preferable that the pressure in the anode chamber 22 and the pressure in the cathode chamber 24 are approximately the same, but if the difference between the pressure in the anode chamber 22 and the pressure in the cathode chamber 24 becomes too large, the anode gas will flow over the partition wall 17 into the cathode chamber 24, causing a reaction between the fluorine gas and the hydrogen gas, which may hinder the generation of fluorine gas. The configuration of the fluorine gas production apparatus of the ninth modified example is substantially the same as that of the fluorine gas production apparatus of the second modified example except for the above points, so a description of the similar parts will be omitted.

[0084] [Tenth Modification] The tenth modified example will be described with reference to Fig. 13. In the fluorine gas production apparatus of the tenth modified example, a first average particle diameter measuring unit 31 is provided in the electrolytic cell 11, and the anode gas inside the electrolytic cell 11 is directly introduced into the first average particle diameter measuring unit 31 to measure the average particle diameter of the mist. The fluorine gas production apparatus of the tenth modified example does not have a second average particle diameter measuring unit 34. Except for the above points, the configuration of the fluorine gas production apparatus of the tenth modified example is substantially the same as that of the ninth modified example shown in Fig. 12, and therefore a description of the similar parts will be omitted. EXAMPLES

[0085] The present invention will be described more specifically below with reference to examples and comparative examples. [Reference example 1] Fluorine gas was produced by electrolyzing the electrolyte. A mixed molten salt (560 L) of 434 kg of hydrogen fluoride and 630 kg of potassium fluoride was used as the electrolyte. Amorphous carbon electrodes (30 cm wide, 45 cm long, 7 cm thick) manufactured by SGL Carbon were used as anodes, and 16 anodes were placed in the electrolytic cell. A punched plate manufactured by Monel (trademark) was used as a cathode, and was placed in the electrolytic cell. Two cathodes faced one anode, and the total area of ​​the part of one anode facing the cathode was 1736 cm. 2 It is.

[0086] The electrolysis temperature was controlled at 85 to 95°C. First, the electrolyte temperature was set to 85°C, and the current density was 0.036 A / cm 2 A direct current of 1000 A was applied at 400 rpm to start electrolysis. The water concentration in the electrolytic solution at this time was 1.0 mass %. The water concentration was measured by Karl Fischer analysis. Electrolysis was started under the above conditions, and a small popping sound was observed near the anode in the anode chamber from immediately after the start of electrolysis until the cumulative current flow reached 10 kAh. This popping sound was thought to be caused by a reaction between the generated fluorine gas and the moisture in the electrolyte. When the intensity of this popping sound was measured, the average value was 50 dB, and the maximum value was 70 dB.

[0087] The fluid generated at the anode in this state was sampled when it was sent out from the anode chamber of the electrolytic cell, and the mist contained in the fluid was analyzed. As a result, it was found that 5.0-9.0 mg of powder (calculated assuming that the specific gravity of the mist was 1.0 g / mL; the same applies below) was contained per liter of fluid generated at the anode, and the average particle size of this powder was 1.0-2.0 μm. When this powder was observed under an optical microscope, it was found that the majority of the powder had a shape resembling a sphere with the inside hollowed out. The current efficiency of fluorine gas generation at this time was 0-15%.

[0088] Furthermore, when electrolysis was continued until the cumulative current flow reached 30 kAh, the frequency of popping sounds occurring inside the anode chamber decreased. The intensity of the popping sounds was measured, and the average value was 25 dB, with a maximum value of 35 dB. The water concentration in the electrolyte at this time was 0.7 mass%. In addition, the fluid generated at the anode in this state was sampled at the point where it was sent out from the anode chamber of the electrolytic cell to the outside, and the mist contained in the fluid was analyzed. As a result, 0.4 to 1.0 mg of mist was contained per 1 L of the fluid generated at the anode, and the average particle diameter of this mist was 0.5 to 0.7 μm. Furthermore, the current efficiency of fluorine gas generation at this time was 15 to 55%. The stage of electrolysis from the start of electrolysis to this point is referred to as "stage (1)".

[0089] Furthermore, electrolysis of the electrolyte was continued following stage (1). As a result, hydrogen fluoride was consumed and the level of the electrolyte decreased, so hydrogen fluoride was appropriately replenished from the hydrogen fluoride tank to the electrolytic cell. The water concentration in the replenished hydrogen fluoride was 500 mass ppm or less. When electrolysis was continued and the cumulative current flow exceeded 60 kAh, the average particle size of the mist contained in the fluid generated at the anode became 0.36 μm (i.e., 0.4 μm or less). At this point, the average measured value of the intensity of the popping sound was 15 dB, with a maximum value of 30 dB. The water concentration in the electrolyte at this time was 0.2 mass% (i.e., 0.3 mass% or less). Furthermore, the current efficiency of fluorine gas generation at this time was 65%. The stage of electrolysis from the end of stage (1) to this point is referred to as "stage (2)".

[0090] Furthermore, the current was increased to 3500A and the current density was reduced to 0.126A / cm 2 The current flow rate was increased to 0.03 to 0.06 mg per liter of fluid generated at the anode, and electrolysis of the electrolyte was continued from stage (2). The fluid generated at the anode in this state was sampled at the point where it was sent out from the anode chamber of the electrolytic cell, and the mist contained in the fluid was analyzed. As a result, 0.03 to 0.06 mg of powder was contained per liter of fluid generated at the anode, and the average particle size of this powder was about 0.2 μm (0.15 to 0.25 μm), with a particle size distribution of about 0.1 to 0.5 μm. Figure 14 shows the measurement results of the particle size distribution of this powder. Furthermore, the current efficiency of fluorine gas generation at this time was 94%. At this point, the measured values ​​of the intensity of the popping sound were 2 dB on average and 5 dB at maximum. The electrolysis stage from the end of stage (2) to this point is called the "stable stage."

[0091] The details of the electrolysis of Reference Example 1 carried out as described above are summarized in Table 1. Table 1 shows the current, electrolysis time, amount of current, water concentration in the electrolyte, mass of mist contained in 1 L of the fluid generated at the anode (referred to as "anode gas" in Table 1), average particle size of the mist, and current efficiency, as well as the amount of the fluid generated at the anode (containing fluorine gas, oxygen gas, and mist), the amount of mist generated at the anode, the intensity of the popping sound, and the water concentration in the fluid generated at the cathode (referred to as "water concentration in cathode gas" in Table 1).

[0092] Moreover, a graph showing the relationship between the average particle size of the mist and the amount of mist generated at the anode is shown in Figure 15. From the graph in Figure 15, it can be seen that there is a correlation between the average particle size of the mist and the amount of mist generated at the anode. The more mist is generated, the more likely it is that piping and valves will become clogged, and when mist with an average particle size larger than 0.4 μm is generated, the amount of mist generated increases and is further deposited by the action of gravity, so it can be said that the relationship shown in the graph in Figure 15 represents a correlation between the average particle size of the mist and the likelihood of piping and valves becoming clogged.

[0093] Furthermore, a graph showing the relationship between the average particle size of the mist and the intensity of the popping sound is shown in Figure 16. Since the larger the average particle size of the mist, the more likely it is that pipes and valves will become clogged, it can be said that the relationship shown in the graph in Figure 16 represents a correlation between the intensity of the popping sound generated near the anode inside the electrolytic cell due to the electrolysis of the electrolyte during electrolysis and the likelihood of pipes and valves becoming clogged.

[0094] [Table 1]

[0095] Example 1 Electrolysis similar to that in Reference Example 1 was carried out using the fluorine gas production apparatus shown in Fig. 2. In the electrolysis in stage (1), the fluid generated at the anode was circulated through the second bypass pipe, the bypass valve, and the first bypass pipe. After the electrolysis in stage (1) was completed, the electrolysis was temporarily stopped, and the inside of the fluorine gas production apparatus was inspected. As a result, although mist had accumulated in the first bypass pipe, no blockage of the pipe occurred because the diameter of the pipe was made large.

[0096] Since the electrolysis reached stage (2) where the average particle size of the mist was 0.4 μm or less (the intensity of the popping sound near the anode was 15 to 30 dB, which is below the standard value of 30 dB), the fluid generated at the anode was circulated through the first pipe, the first pipe valve, the fourth pipe, and the first mist removal section. No accumulation or blockage of mist occurred in the first pipe, the first pipe valve, or the fourth pipe, and the fluid generated at the anode was supplied to the first mist removal section, so the mist was removed in the first mist removal section. The first mist removal section is a scrubber-type removal section that sprays liquid hydrogen fluoride to remove fine particles such as mist, and the mist removal rate was 98% or more.

[0097] Comparative Example 1 In the electrolysis in step (1), electrolysis was performed in the same manner as in Example 1, except that the fluid generated at the anode was circulated through the first pipe, the first pipe valve, the fourth pipe, and the first mist removal section. During electrolysis in stage (1), the pressure gauge attached to the anode and cathode sides of the electrolytic cell gradually increased in value on the anode side, and the pressure difference with the cathode side reached 90 mmH2O, so electrolysis was stopped. The reason for the stoppage is as follows. The vertical length (immersion depth) of the part of the partition in the electrolytic cell that was immersed in the electrolyte was 5 cm, so when the pressure on the anode side became approximately 100 mmH2O higher than the pressure on the cathode side, the liquid level of the electrolyte on the anode side became lower than the bottom end of the partition. As a result, the fluorine gas overcame the partition and mixed with the hydrogen gas on the cathode side, causing a rapid reaction between the fluorine gas and hydrogen gas, which was extremely dangerous. After purging the system with nitrogen gas, etc., the inside of the first pipe, the first pipe valve, and the fourth pipe were inspected, and it was found that the first pipe was not clogged because it is a vertical pipe. There was a small amount of powder attached to the first pipe valve, and the pipe downstream of the first pipe valve, i.e., the inlet to the fourth pipe, was clogged with powder. There was also powder accumulation in the fourth pipe, but the amount was not enough to clog the pipe. [Explanation of symbols]

[0098] 1. Sample chamber 2...Light source 3. Scattered light detection unit 4A, 4B: Transparent window 10...electrolyte 11...Electrolytic cell 13...Anode 15...Cathode 22...Anode chamber 24 Cathode chamber 31...1st average particle size measuring section 32... First mist removal section 33 Second mist removal section 34...Second average particle size measuring section 37 Sound intensity measurement section 41...First pipe 42...Second piping 43 Third pipe 44... 4th pipe 45···5th pipe 46...6th pipe 47 No. 7 Pipe 48. No. 8 Pipe 49. No. 9 Pipe 51 First bypass pipe 52 Second bypass piping 61...First piping valve 62 Bypass valve F...Fluid L...Light for light scattering measurement M...Mist S...scattered light

Claims

1. A method for producing fluorine gas, comprising electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride to produce fluorine gas, comprising the steps of: an electrolysis step in which the electrolysis is carried out in an electrolytic cell; a sound intensity measuring step of measuring the intensity of sound generated in the vicinity of the anode inside the electrolytic cell in association with the electrolysis of the electrolyte during the electrolysis; a gas supplying step of supplying a fluid generated in the electrolytic cell during electrolysis of the electrolytic solution from the inside of the electrolytic cell to the outside of the electrolytic cell through a flow path; Equipped with In the gas supplying step, a flow path through which the fluid flows is switched in accordance with the intensity of the sound measured in the sound intensity measuring step. When the intensity of the sound measured in the sound intensity measuring step is equal to or less than a preset reference value, the fluid is supplied to a first flow path through which the fluid is supplied from inside the electrolytic cell to a first outside, and when the intensity of the sound measured in the sound intensity measuring step is greater than the preset reference value, the fluid is supplied to a second flow path through which the fluid is supplied from inside the electrolytic cell to a second outside. A method for producing fluorine gas, wherein the preset reference value is a value within a range of 10 dB or more and 60 dB or less.

2. 2. The method for producing fluorine gas according to claim 1, wherein the metal fluoride is a fluoride of at least one metal selected from the group consisting of potassium, cesium, rubidium, and lithium.

3. 3. The method for producing fluorine gas according to claim 1, wherein the anode used in the electrolysis is a carbonaceous electrode made of at least one carbon material selected from the group consisting of diamond, diamond-like carbon, amorphous carbon, graphite and glassy carbon.

4. 4. The method for producing fluorine gas according to claim 1, wherein the electrolytic cell has a structure that enables bubbles generated at an anode or a cathode used in the electrolysis to rise vertically in the electrolytic solution and reach the liquid surface of the electrolytic solution.

5. A fluorine gas production apparatus for producing fluorine gas by electrolyzing an electrolyte solution containing hydrogen fluoride and a metal fluoride, comprising: an electrolytic cell containing the electrolytic solution and in which the electrolysis is carried out; a sound intensity measuring unit that measures the intensity of sound generated in the vicinity of the anode inside the electrolytic cell in association with the electrolysis of the electrolyte during the electrolysis; a flow path for transporting a fluid generated in the electrolytic cell during electrolysis of the electrolytic solution from the inside to the outside of the electrolytic cell; Equipped with the flow path includes a first flow path for sending the fluid from inside the electrolytic cell to a first outside, and a second flow path for sending the fluid from inside the electrolytic cell to a second outside, and includes a flow path switching unit for switching the flow path for the fluid between the first flow path and the second flow path in response to the sound intensity measured by the sound intensity measuring unit, the flow path switching unit sends the fluid from inside the electrolytic cell to the first flow path when the sound intensity measured by the sound intensity measuring unit is equal to or less than a preset reference value, and sends the fluid from inside the electrolytic cell to the second flow path when the sound intensity measured by the sound intensity measuring unit is greater than the preset reference value, The preset reference value is a value within a range of 10 dB or more and 60 dB or less.

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